It's no secret that apples and pork go great together. Slideshow: More Crock Pot and Slow Cooker Recipes
Score the skin of the pork with a sharp knife. Make 1-inch deep incisions with a paring knife all over the pork and insert 1 slice of garlic in each incision. Season the pork with 1 1/2 teaspoons salt and 3/4 teaspoon pepper. In a 5-to 6-quart crock pot, heat the oil over high heat until hot. Sear the pork butt, turning once, until browned, 6 to 8 minutes total. Transfer the pork to a plate and stir the onion into the crock pot. Brown the onion, scraping up any browned bits, until golden, about 6 minutes. Place the pork back in the crockpot along with the cider and cover the crock pot.
Simmer the pork butt on low, covered, until the meat is very tender, 7 to 8 hours. Shred the pork, discarding the bone, then place the shredded pork back in the cooking liquid. Season with salt and pepper to taste and serve with rolls.